docs: def nn_y(self, y, k=1, radius=np.inf, eps=0.0, p=2):
          """Find the k nearest neighbors of y in the observed output data
          @see Databag.nn() for argument description
          @return  distance and indexes of found nearest neighbors.
          """
          assert len(y) == self.dim_y
          k_y = min(k, self.size)
          return self._nn(DATA_Y, y, k=k_y, radius=radius, eps=eps, p=p)